The present invention relates generally a safety device for elevators to prevent unintended elevator car movement.
For guiding the elevator car in the case of elevators with guide rails, guide shoes, which are arranged at the elevator car, are employed and such guide shoes are developed either as roller guide shoes or as sliding guide shoes. In the first case, rollers are generally provided with so-called two-dimensional or three-dimensional guides, which roll on appropriate guide surfaces of the guide rail. In the second case, slideway linings slide with small free motion along the guide rails, so that they confer to the elevator car during the vertical transport motion a guide in the horizontal plane. Safety devices, which are physically separate from the guide shoes, are fastened to the elevator car and such safety devices operate to engage the guide rail.
The well-known devices of this kind work in the manner that in case of exceeding the speed limit of the elevator car or respectively in case of over-speed, the safety device is mechanically operated by a speed governor device.
The common safety devices of the state of the art can be categorized according to their construction either to the group of the brake safety devices or the group of the wedge blocking safety devices or the roller blocking safety devices.
A brake safety device is shown in the U.S. Pat. No. 6,131,704, which has a slideway for guiding the elevator car along the guide rail. This safety device includes a forked lever mechanism and a relatively large and heavy electromagnet. With this safety device, the guiding apparatus is functionally separated from the braking device or respectively from the safety device. The usage of such a safety device is therefore uneconomical in particular in the case of low cost elevators with small hoisting height, that is to say for buildings with few floors and low hoisting speeds of the elevator car.
In the case of wedge blocking safety devices or roller blocking safety devices, a loose wedge or loose roller is engaged on a side of the guide rail in order to fit between the stationary guide rail on the one hand and an associated abutment of the safety device on the other hand, by means of the speed limiter, while the safety device block is supported on the opposite side of the guide rail. The prevailing frictional circumstances lead to a further blocking of the clamp body or respectively of the blocking roller and consequently to the braking of the elevator car. Such a blocking roller safety device is described for example in the published European application EP 0 870 719 A1.
Conventional safety devices are applied only in the case of over-speed or in case of inspection work (typically twice per year). Traditional safety devices are in particular of major disadvantage if the elevator car stands at a floor and due to loading, it slips or it falls uncontrolled.
According to the state of the art, an additional so-called creeping protection device prevents the slipping of the elevator car. Thereby, a bolt is pushed into engagement, for example in the appropriate openings of the guide rail, during each stop at a floor, so as to hold in each case the elevator car at the floor level. Further details about the construction and the function of such a creeping protection device are shown in the published European application EP 1 067 084 A1.
A task of the following described invention is therefore to avoid the mentioned disadvantages of the state of the art devices and to create an improved safety device for elevators.